Fields are already known that deal with viscous materials. Such applications include sealants for mechanical or electrical components, encapsulants, coating agents, grease, resin compositions (e.g., epoxy resins), adhesives, pastes for use in forming electrical or electronic circuits, solders for use in mounting electronic components, etc. Such viscous materials are used in, for example, the aerospace industry, the electrical industry, the electronics industry, etc.
In order to apply a viscous material to a desired target, dispensers are used that discharge a viscous material. An example thereof is a mechanical dispenser that dispenses a viscous material by pressing a plunger using a mechanical force; another example is a pneumatic dispenser that dispenses a viscous material by pressing a plunger using pressurized gas; yet another example is an electronic dispenser that dispenses a viscous material by pressing a plunger using an electric motor.
Hereinbelow, although drawbacks of known cartridges for viscous-material dispensers will be described in detail by using a pneumatic dispenser as an example, persons skilled in the art can easily imagine the same drawbacks existing in other types of dispensers, such as for example, in the mechanical dispenser and the electronic dispenser mentioned above; in addition, persons skilled in the art can easily imagine the same drawbacks existing in still other types of dispensers, such as for example, a dispensing syringe.
Generally speaking, a cartridge is configured to be exchangeably loaded into a pneumatic dispenser, which is assembled by fitting a plunger or a piston in a cylinder. As a result of the fitting, an inner chamber of the cylinder is divided into a filling chamber, into which the viscous material is filled from outside of the filling chamber (i.e., an example of an “anterior chamber” described later), and a pressurizing chamber (i.e., an example of a “posterior chamber” described later) into which the pressurized gas is introduced from outside of the pressurizing chamber.
In order to discharge the viscous material towards a desired target using a pneumatic dispenser of this type, it is first necessary to fill the filling chamber in the cylinder of the pneumatic dispenser with the viscous material. Following the filling, the viscous material is discharged towards the desired target by applying pressure to the plunger in the pneumatic dispenser using the pressurized gas in the pressurizing chamber.
The co-inventors repeatedly performed experiments in which a viscous material is filled into a conventional cartridge assembled by fitting a conventional plunger in a cylinder, and after completion of the filling, the cartridge is attached to a pneumatic dispenser and the viscous material is discharged from the pneumatic dispenser.
As a result, the co-inventors obtained the following insights. That is, in the filling stage, it is important to simultaneously fulfill: the need (intended air venting or degassing of the viscous material) to vent air, which is present in a filling chamber, by passing it through a clearance between the plunger and the cylinder, and the need (viscous material leakage prevention) to create, after completion of the air venting, a seal between the plunger and the cylinder, to thereby prevent the viscous material from leaking from the filling chamber into the pressurizing chamber.
In addition, in the discharging stage, it is important to create a seal between the plunger and the cylinder, to thereby prevent the ingress of the pressurized gas from the pressurizing chamber into the filling chamber (pressurized air leakage prevention). An unintended leakage of the pressurized gas from the pressurizing chamber into the filling chamber could cause a problem that the pneumatic dispenser fails to expel the viscous material properly, and a problem that the pressurized gas unintentionally enters the filling chamber, in which the viscous material is stored as a material to be expelled next, and gas bubbles are entrapped in the viscous material within the filling chamber.
To achieve the demands described above, the co-inventors developed a new plunger. This plunger is disclosed in Patent Document No. 1.
More specifically, at least two lands are formed on an outer circumferential surface of this plunger such that each land extends circumferentially. These lands include a first land proximal to the filling chamber, and a second land proximal to the pressurizing chamber. Since the second land is larger in diameter than the first land, a radial clearance created between the top surface of the second land and an inner circumferential surface of a cylinder is smaller than that created between the top surface of the first land and the inner circumferential surface of the cylinder.
This plunger is fitted within the cylinder to provide a cartridge for a pneumatic dispenser; when the cartridge undergoes the filling stage, initially, air within the filling chamber is vented to the pressurizing chamber through clearances between the first land and the cylinder and between the second land and the cylinder.
Upon completion of the air venting (i.e., degassing of the viscous material), a portion of the viscous material within the filling chamber passes through a radial clearance between the plunger and the cylinder upstream of the first land, and reaches the first land, thereby completing the creation of a first seal between the first land and the cylinder. In other words, a portion of the viscous material that is to be used for the filling forms the first seal.
With time, another portion of the viscous material reaches the second land, thereby creating a second seal between the second land and the cylinder. In other words, another portion of the viscous material that is to be used for the filling forms the second seal. In the filling stage, after the first and second seals are completed, the viscous material is prevented from leaking from the filling chamber to the pressurizing chamber.
In the ensuing discharging stage, from its beginning, both the first and second seals are completed. As a result, pressurized gas, once introduced into the pressurizing chamber, is blocked by the second seal. This prevents the pressurized gas from leaking from the pressurizing chamber into the filling chamber.
Patent Document No. 1: Japanese Patent No. 5101743